A catheter is commonly used to access an internal body site for either diagnostic or therapeutic purposes. For example, in percutaneous coronary angioplasty, a catheter having a deflated balloon at its distal end is guided through a patient's cardiovascular system to a desired target position within a diseased coronary artery. When in place, the balloon is inflated to compress deposits that have accumulated along the inner walls of the coronary artery. The interior passageway of the artery is thus widened, and blood flow to the heart is increased.
A catheter typically uses a guidewire to aid in placing the catheter at the target site within a blood vessel. A guidewire is typically inserted into a lumen of a balloon catheter, for example, with a distal tip section of the guidewire extending beyond the end of the catheter. The distal tip of the guidewire may be bent at a predetermined angle to facilitate steering of the guidewire to a desired blood vessel at a branch point by selectively rotating a proximal end of the guidewire while viewing the distal tip section by fluoroscopy. The guidewire must be very flexible to navigate bends and turns within the blood vessel, particularly at a distal end portion adjacent the distal tip. The distal end portion of the guidewire may be required to make relatively sharp bends to reach the diseased portion of the coronary artery.
One type of catheter guidewire has a tapered diameter along its length to provide a reduced diameter distal end portion of greater flexibility. In some guidewires, a reduced diameter distal end portion may include a covering of a wound coil to increase the columnar strength and the torque transmitting ability of the guidewire to permit manipulation of the guidewire from the proximal end. See, for example, U.S. Pat. No. 4,676,249 entitled Multi-Mode Guidewire to Arenas et al.; U.S. Pat. No. 4,846,186 entitled Flexible Guidewire to Box et al.; and U.S. Pat. No. 5,001,825 entitled Catheter Guidewire Fabrication Method to Halpern; all of which are assigned to the assignee of the present invention.
U.S. Pat. No. 5,171,383 to Sagaye et al. entitled Method of Manufacturing a Differentially Heat Treated Catheter Guide Wire, discloses a catheter guidewire wherein flexibility is sequentially increased along a highly elastic wire by heat treatment. A thermoplastic resin or coil spring may be applied to the distal end.
Yet another guidewire is disclosed in U.S. Pat. No. 5,095,915 entitled Guidewire with Flexible Distal Tip to Engelson which discloses a guidewire including a wire core having a distal end portion encased in a polymer sleeve extending from the distal tip for a length in the range of from 3 to 25 cm. The polymer sleeve increases the columnar strength of the wire core while, in one embodiment, axially spaced grooves formed in the sleeve provide enhanced flexibility. The sleeve may be formed by extrusion or molding, and secured to the wire core by an adhesive, heat shrinking, or by chemical bonding. Alternately, the sleeve may be formed by dip coating the core wire tip. The grooves in the polymeric sleeve are preferably formed after attachment of the sleeve to the wire core, such as by using a type of lathe.
Unfortunately, many conventional guidewires are not suitable to advance heavier catheters within a blood vessel. For example, conventional guidewires may not be sufficiently flexible, yet resistant to buckling to facilitate placement of a laser, for example, along a tortuous path within a blood vessel. In addition, it may also be advantageous to avoid a guidewire having a polymeric coating and the like on a core wire, because the coating may tend to flake or otherwise separate from the underlying core wire, especially along a length of the guidewire that is repeatedly flexed.